This invention relates to multiple-row roller bearings, particularly large-sized ones, such as used for supporting rolls in rolling mill or for other purposes.
Lately, in order to keep up with increasing speed-up of rolling mills, there is a growing demand for high-performance roll neck roller bearings with high reliability and durability. However, for development of such high-performance bearings, it is required to provide highly effective and secure lubrication for attaining stabilization of performance.
Among the known effective roller bearing lubricating systems is an oil mist lubrication method. According to this method, hot compressed air is supplied into an oil mist generator where the high-viscosity lubricating oil is atomized and injected into the bearing from a nozzle. The atomized lubricating oil, when injected from the nozzle, is turned into coarse particles which are apt to adhere to an object due to fall of temperature caused by adiabatic expansion of air and disturbance of flow caused by injection, and thus dry mist is turned into wet mist. This wet mist impinges against respective parts in the bearing to provide a minimum amount of oil required for sufficient lubrication while that portion of oil which is not required for lubrication is retrieved in the form of floating mist. Thus, the oil mist lubrication system requires only a minimum amount of oil necessitated for lubrication, so that the agitation loss of oil is reduced and also high speed roller bearing lubrication is provided by the cooling action of air.
In the conventional roller bearings, however, above-said merits of the lubricating systems are not necessarily effectuated to the full. That is, in the conventional bearings, in order to prevent oil shortage that is liable to occur at the start of operation, arrangement is made such that the initial charge oil is supplied to the lower portion of the housing so that a part of the bearing will be immersed in the lubricating oil and that there can be maintained a constant oil level. Therefore, this initial charge oil is not discharged but remains in the housing even during operation, and hence even if oil mist lubrication is applied, actual lubrication has mostly depended on the oil bath. Consequently, abnormal rise of bearing temperature that could result in fatal defect to bearing performance would be caused due to increase of agitation loss of oil or increase of agitation heat during high speed rotation.
Particularly in the case of roller bearings, there is produced between the roller end face and the inner race flange face, for the structural reason, a sliding contact portion that takes a share of the thrust load acting in the axial direction, resulting in excessively increased frictional loss as compared with the rolling portion. It was also found that, in the conventional bearings, wet mist impinges against the outer peripheral face of the distance piece and here a substantial portion of mist is condensed and turned into liquid oil, and such oil merely flows down to the lower part of the outer wall of said distance piece, thus little contributing to lubrication. This means that the mist supplied to the lubrication area from the nozzle provided in the distance piece is low in concentration and hence little oil is retrieved in the bearing portion. Consequently, oil shortage would be caused on the roller end faces and inner race flange contact faces which are exposed to the most severe friction conditions, and these parts would often become a heat source causing abnormal rise of temperature.